1. Field of the Invention
The invention relates to a transparent pane, in particular a glass pane, having at least one electroconducting, nontransparent contact surface placed on one of its surfaces, in order to connect it by soldering to a connection piece.
2. Description of Related Art
Such panes are known in many constructions. In most applications, the panes carry, on their surface, electrical functional elements such as electrically conducting tracks, heating surfaces, or antennas, again in the form of coatings over the entire surface, which have to be connected with at least one contact surface to an external connection piece by soldering.
Often the contact surfaces (for example, the conducting tracks or, depending on the case, the functional elements themselves) are produced by applying an electrically conducting paste to be baked; sometimes, thin strips of tinned metal foil are also used, these being connected by soldering to the surface of the pane, which is pretinned where appropriate. In all these cases, a connection piece is applied to the contact surface via the free side and is then soldered.
Many methods of producing composite glazing panels are also known that incorporate electrical functional elements between their rigid panes and are provided, near the edge of the composite glazing panel, with electrical connection pieces to be soldered of the type indicated at the beginning, and of course connection pieces, if possible flat pieces, are used in this case, these having, for example, the structure described in document DE-C2 19 536 131. It has also already been proposed (DE-C1 19 829 151) to supply the heat needed for the soft soldering by induction or laser beam only after a precomposite has been produced. The term “soft soldering” is understood to mean the use of a filler metal for soldering that has a low melting point, one that does not exceed a temperature of 450° C.
As a general rule, the connection pieces to be soldered or the soldering locations themselves are optically masked by means of opaque colored layers. In most standard cases of use as a vehicle window pane, the panes are almost always provided with a peripheral border band in the form of a frame made of a black screen-printing paste that is perfectly suitable for also masking the regions of electrical connections. Said collector rails or actual contact surfaces are also not transparent because they are made of a screen-printing paste with a high silver content or, as was indicated, in the form of bands of metal foil. On the passenger compartment side of the vehicle, the border regions of the panes and the mounting flanges on the body that bear them are usually covered and masked by interior furnishing elements.
In general, for transparent panes provided with contact surfaces, in particular for the soldering places located on the inside of a composite glazing panel, which are heated only after this composite has been manufactured, the problem arises of being able to reliably check the result of the soldering through the pane.
Although document EP-B1-281 351 describes one particular illustrative example of such soldering locations, in which a framed contact surface is produced on an opaque coating of the surface of a glass pane using a special screen-printing pattern on the structure of which the liquid soldering filler metal can adhere better, visual inspection of these soldering places is possible only from the free side of the pane; because of the opaque coating, the rear side of the contact surface is not visible through the actual pane.
The problem at the basis of the invention consists in proposing a solution to the abovementioned problem.